[ECR] [request]: Allow cross-region and cross-account replication to copy immutability, image scanning & KMS encryption settings

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**Tell us about your request**
What do you want us to build?
Allow cross-region and cross-account replication to copy immutability, image scanning KMS encryption settings

**Which service(s) is this request for?**
ECR

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Our use-case involves hundreds of repos to be replicated across multiple regions and to multiple accounts. Enabling these settings manually seems to be error prone and daunting. we wanted a native solution within ECR instead of incorporating other solutions/resources around it.

**Are you currently working around this issue?**
Currently we are manually enabling these settings. planning to setup Lambda function to perform the same in near future.

Start by reviewing the ECR cross-region and cross-account replication behavior described in the request. Determine how repository immutability, image scanning, and KMS encryption settings are currently configured and what native replication support would need to copy. Done means those settings are replicated reliably across the requested regions and accounts.

Written by the indexing model from the issue text.